1. Field of the Invention
The present invention relates to a multi-outputting power supply circuit including a main-output circuit section and at least one sub-output circuit section, and more particularly, to the multi-outputting power supply circuit, in which, the sub-output circuit section is controlled by a magnetic amplifier.
The present application claims priority of Japanese Patent Application No. 2000-149127 filed on May 19, 2000, which is hereby incorporated by reference.
2. Description of the Related Art
As shown in FIG. 11, this kind of a conventional multi-outputting power supply circuit 100 is mainly made up of an input circuit section 1, a transformer 2, a main-output circuit section 3, and a plurality of sub-output circuit sections 4, 5, . . .
The input circuit section 1 is provided with a direct current power supply section 1a, an input smoothing capacitor 1b, a PWM (Pulse width Modulation) controlling circuit 1c, and a main-switch made up of for example, an N channel type MOS transistor (hereinafter may be referred to as NMOS 1d). The transformer 2 includes a primary winding 2a connected with input circuit section 1, a plurality of secondary windings 2b, 2c, 2d, connected respectively with sub-output circuit sections 4, 5, . . . .
The main output circuit section 3 is provided with a first diode 3a, a smoothing choke coil 3b, a second diode 3c, a smoothing capacitor 3d, a dummy resistor 3e, and a constant-voltage controlling circuit 3f, thus supplying an electric power to a load RL1. The sub-output circuit section 4 is provided with a magnetic amplifier 4a, the third diode 4b, a smoothing choke coil 4c, the fourth diode 4d, a smoothing capacitor 4e, a constant-voltage controlling circuit 4f, resistors 4g and 4h, a transistor 4I, and diode 4j. The sub-output circuit section is connected to a load RL2. The sub-output circuit section 5 is the same structure as the sub-output circuit section 4, and is connected to a load RL3. And the multi-outputting power supply circuit may be provided with a electric dummy circuit 3g as shown in FIG. 12 instead of a dummy resistor 3e. The electric dummy circuit 3g is provided with a resistor 3h, a NMOS 3I, an output electric current detecting circuit 3j, and resistor 3k, and becomes ON state so as to flow dummy electric current through a resistor 3h only when a load is light.
With the above configuration, main output circuit section 3 is capable of outputting more electric power under less load variation than any sub-output power sections 4, 5, . . . .
And a duty ratio of switching in a primary side (input circuit section 1) is controlled by a negative feedback signal fed to the primary side, based on an output voltage variation of a secondary side (main output circuit section 3).
In each of sub-output circuit sections 4, 5, . . . , magnetic amplifier 4a controls an alternating current voltage having a specified duty ratio based on an output voltage fed from main output circuit section 3, hereby producing output voltage having a specified level.
Next, an operation principle of magnetic amplifier 4a will be described in detail, with reference to FIGS. 13 and 14.
FIGS. 13 and 14 are illustration for explaining an operation principle of the magnetic amplifier 4a as shown in FIG. 11.
As shown in FIG. 14, when a pulse electric current with a pulse widthxc3x97xcexcs flows, the magnetic amplifier 4a is an ON state. Here, even if the pulse electric current repeats a shifting between the ON state and an OFF state, a magnetic state of a magnetic amplifier 4a will can only go and back between a point A and a point B, in which, the point A corresponds to a maximum value of pulse current and the point B corresponds to a magnetic field zero or an electric current zero, and the magnetic amplifier 4a remains in the on state. However, while pulse electric current is the OFF state, because a slight electric current (that is to say, reset current) flows through the magnetic amplifier 4a in the opposite direction to the pulse electric current, a magnetic state of a magnetic amplifier 4a shifts to a point C, and the magnetic amplifier 4a becomes in the OFF state. In this state, even if a voltage E is supplied to the magnetic amplifier 4a in the positive direction, electric current does not flow at once, however, the electric current begins to flow after xcex94T time.
xcex94T is obtained by the following formula.
Magnetic flux (xcfx86)=The product of voltage and Time (Exc3x97T)xe2x80x83xe2x80x83Equation 1
xcex94T=xcex94xcfx86/Exe2x80x83xe2x80x83Equation 2
PWM is executed by controlling the xcex94T by the reset current. Here, when the following formula is satisfied, the current does not flow at all.
X=xcex94Txe2x80x83xe2x80x83Equation 3
That is to say, PWM is executed at range from 0 to 100 percent by adjusting a width of xcex94xcfx86 of magnetic amplifier 4a. 
In the multi-outputting power supply circuit 100, the direct current input power voltage V1a is produced in the direct current power section 1a, and is output. The direct current input power voltage V1a is smoothed by the input smoothing capacitor 1b. A control signal V1c with a pulse width corresponding to a fixed frequency and a detective signal V3f is produced. The direct current input power voltage V1a is controlled for an ON or OFF state so as to produce an alternating current voltage V1d with a pulse width corresponding to a fixed frequency and detective signal V3f. The alternating current voltage V1d is transformed by the transformer 2 so as to produce an alternating current voltage V2b and the alternating current voltage V2c, V2d. 
The alternating current voltage V2b is smoothed by the first diode 3a so as to produce a pulsating voltage V3a. Electromagnetic energy of the pulsating voltage V3a is stored in the smoothing choke coil 3b. When the first diode 3a becomes in an OFF state and the second diode 3c becomes in an ON state, the electromagnetic energy is then supplied to the smoothing capacitor 3d. The pulsating voltage V3a is smoothed by the smoothing capacitor 3d so as to produce a direct current output power voltage V3. The direct current output power voltage V3 is supplied to the dummy resistor 3e and the load RL1. When the direct current output power voltage V3 changes, the constant-voltage controlling circuit 3f detects a change of the direct current output power voltage V3 so as to produce the detective signal V3f. The detective signal V3f is supplied to the PWM controlling circuit 1c, and a pulse width of the alternating current voltage V1d is controlled for negative feed-back by the PWM controlling circuit 1c. 
The alternating current voltage V2c according to a turn ratio between the primary winding 2a and the secondary winding 2c is produced based on a duty ratio predetermined by the PWM controlling circuit 1c at the secondary winding 2b of the transformer 2. The alternating current voltage V2c is smoothed by the third diode 4b through the magnetic amplifier 4a so as to produce a pulsating voltage V4b. The electromagnetic energy of the pulsating voltage V4b is stored in the smoothing choke coil 4c. When the third diode 4b becomes in an OFF state and the fourth diode 4d becomes in an ON state, the electromagnetic energy is supplied to the smoothing capacitor 4e. The pulsating voltage V4b is smoothed by the smoothing capacitor 4e so as to produce a direct current output power voltage V4. And a direct current output power voltage V4 is output from the sub-output circuit section 4 to the load RL2. Stabilizing the direct current output power voltage v4 is performed by using a hysteres is characteristic of the magnetic amplifier 4a. That is to say, a change of the direct current output power voltage V4 is detected with resistors 4g and 4h, and the reset current, is for the magnetic amplifier 4a being necessary to stabilize the direct current output power voltage V4, is adjusted by the constant voltage controlling circuit 4f, and while a magnetic amplifier 4a is in an OFF state, the reset current flows to the magnetic amplifier 4a. A rise time of a during of the ON state of a magnetic amplifier 4a is controlled so as to stabilize the direct current output power voltage V4. In the sub-output circuit section 5, the same operation as the sub-output circuit section 4 is performed.
However, a conventional multi-outputting power supply circuit 100 has the following problem, that is to say, if the conventional multi-outputting power supply circuit 100 is not provided with the dummy resistor 3e, the load RL1 connected to the main-output circuit section 3 becomes, for example, light as in no-load, and when the load electric current becomes below a threshold electric current of the smoothing choke coil 3b, the energy stored in the smoothing choke coil 3b is stored in the smoothing capacitor 3d, therefore the direct current output power voltage V3 increases. The time width of an ON state of the magnetic switch 1d (NMOS), is controlled to become narrow for the purpose of suppressing a rise of the direct current output voltage V3. In this case, because a pulse width of the alternating current voltage V2c produced in the second winding 2c becomes narrow, the product of voltage and time (the product of VT) is not ensured. Therefore, the direct current output power voltage V4 may be not stable. On condition that V is a voltage between two terminals of the magnetic amplifier 4a, T is time to saturate the magnetic amplifier 4a. For the purpose of solving the problem, the necessary product of voltage and time is ensured by putting the dummy resistor 3e in the main-output circuit section 3 and preventing a narrowing of a time width in an On state of a main switch 1d (NMOS). Accordingly, there has been a problem that electric power is always consumed, and a efficiency of a power source goes down. And there is another problem that the number of parts increases because the dummy resistor 3e, a radiator( not shown) radiating heat of the dummy resistor 3e and the like, or a electric dummy circuit 3g (shown in FIG. 12) are required.
In view of the above, it is an object of the present invention to provide a multi-outputting power supply circuit capable of producing stably a direct current output voltage of a sub-output circuit section without a dummy resistor and an electric dummy circuit in a main-output circuit section.
According to a first aspect of the present invention, there is provided a multi-outputting switching power supply circuit including:
a main-output circuit section;
at least one sub-output circuit section; and
wherein the at least one sub-output circuit section is controlled by a magnetic amplifier for amplifying electric power magnetically and the main-output circuit section has a synchronous rectifying circuit made up of a MOS transistor, whereby, a dummy load is omitted.
According to a second aspect of the present invention, there is provided a multi-outputting switching power supply circuit including:
a main-output circuit section having a smoothing choke coil;
at least one sub-output circuit section controlled by a magnetic amplifier for amplifying electric power magnetically; and
wherein the main-output circuit section has a synchronous rectifying circuit made up of a MOS transistor, whereby, a dummy load is omitted.
According to a third aspect of the present invention, there is provided a multi-outputting switching power supply circuit including:
a direct current power supply section for producing a direct current input voltage;
a switching circuit for producing, by controlling the direct current input voltage for an ON or an OFF state based on an input control signal, a first alternating current voltage having a fixed frequency controlled by the control signal and a pulse width corresponding to the control signal;
a transformer for producing, by transforming the first alternating current voltage, a second alternating current voltage with a fixed voltage value and at least one third alternating current voltage;
a first rectifying circuit for producing, by rectifying the second alternating current voltage, a first pulsating voltage;
a first smoothing circuit for producing, by smoothing the first pulsating voltage, a first direct output voltage so as to supply the first direct current output voltage to a load;
a voltage change detecting circuit for producing, by detecting a change of the first direct current output voltage, a detective signal;
a controlling circuit for producing the control signal to control a pulse width of the first alternating current voltage for negative feed-back according to a level of the detective signal;
at least one magnetic amplifier for producing a fourth alternating current voltage for producing, by controlling the third alternating current voltage for an ON or an OFF state based on the reset electric current, a fourth alternating current voltage with a pulse width corresponding to a reset electric current;
at least one second rectifying circuit for producing, by rectifying the fourth alternating current voltage, a second pulsating voltage;
at least one second smoothing circuit for producing, by smoothing the pulsating voltage, a second direct current output voltage so as to supply the second direct current output voltage to a load;
at least one voltage controlling circuit for producing, by detecting a change of the second direct current output voltage, the reset electric current to control the fourth alternating current voltage for negative feed-back; and
wherein the first rectifying circuit includes a switching circuit for producing the first pulsating voltage by controlling the second alternating current voltage for an ON or an OFF state, synchronizing with a timing of switching in the switching circuit.
In the foregoing, a preferable mode is one wherein the switching circuit is provided with a MOS transistor for producing, by controlling the second alternating current voltage for the ON or the OFF state, synchronizing with a change of polarity of the second alternating current voltage, the first pulsating voltage.
According to a fourth aspect of the present invention, there is provided a multi-outputting switching power supply circuit including:
a direct current power supply section for producing a direct current input voltage;
a switching circuit for producing, by controlling the direct current input voltage for an ON or OFF state based on the input control signal, a first alternating current voltage having a fixed frequency controlled by a control signal and a pulse width corresponding to a control signal;
a transformer for producing, by transforming the first alternating current voltage, a second alternating current voltage with a fixed voltage value and at least one third alternating current voltage;
a first rectifying circuit for producing, by rectifying the second alternating current voltage, a first pulsating voltage;
a first smoothing circuit for producing, by smoothing the first pulsating voltage, a first direct current output voltage so as to supply the first direct current output voltage to a load;
a voltage change detecting circuit for producing, by detecting a change of the first direct current output voltage, a detecting signal;
a controlling circuit for producing the control signal to control a pulse width of the first alternating current voltage for negative feed-back based on a level of the detective signal;
at least one magnetic amplifier for producing, by controlling the third alternating current voltage for an ON or an OFF state based on the reset electric current, a fourth alternating current voltage with a pulse width corresponding to a reset electric current;
at least one rectifying circuit for producing, by rectifying the fourth alternating current, a second pulsating voltage;
at least one smoothing circuit for producing, by smoothing the second pulsating voltage, a second direct current output voltage so as to supply the second direct current voltage to a load;
at least one voltage controlling circuit for producing, by detecting a change of the second direct current output voltage, the reset electric current to control the fourth alternating current voltage for negative feed-back; and
wherein the first rectifying circuit is provided with a first switching circuit for producing, by controlling the second alternating current voltage for an ON or an OFF state, synchronizing with a timing of switching in the switching circuit, the first pulsating voltage, wherein the first smoothing circuit is provided with a smoothing capacitor for producing, by smoothing the first pulsating voltage, the first direct current output voltage, so as to supply the first direct current output voltage to a load, a choke coil for storing an electromagnetic energy caused by the pulsating voltage, a second switching circuit supplying the electromagnetic energy stored in the choke coil to the smoothing capacitor by becoming in an ON state when the first switching circuit is in an OFF state.
In the foregoing, a preferable mode is one wherein the first and second switching circuit are made up of a MOS transistor.
According to a fifth aspect of the present invention, there is provided a multi-outputting switching power supply circuit including:
a direct current power supply section for producing a direct current input voltage;
a switching circuit for producing, by controlling the direct current input voltage for an ON or OFF state based on the input control signal, a first alternating current voltage having a fixed frequency controlled by a control signal and a pulse width corresponding to the control signal;
a transformer for producing, by transforming the first alternating current voltage, a second alternating current voltage with a fixed voltage value and at least one third alternating current voltage;
an active clamp circuit for resetting a core of the transformer by flowing an excitation current through a primary winding of the transformer while the switching circuit is in the OFF state;
a first rectifying circuit for producing a first pulsating voltage by rectifying the second alternating current voltage;
a first smoothing circuit for producing, by smoothing the first pulsating voltage, a first direct current output voltage so as to supply the first direct current output voltage to a load;
a voltage change detecting circuit for producing, by detecting a change of the first direct current output voltage, a detective signal;
a controlling circuit for producing the control signal to control a pulse width of the first alternating current voltage for negative feed-back based on a level of the detective signal;
at least one magnetic amplifier for producing, by controlling the third alternating electric current for an ON or an OFF state based on the reset electric current, a fourth alternating current voltage with a pulse width corresponding to a reset electric current;
at least one second rectifying circuit for producing, by rectifying the fourth alternating current voltage, a second pulsating voltage;
at least one smoothing circuit for producing, by smoothing the second pulsating voltage, a second pulsating voltage so as to supply the second direct current output voltage to a load;
at least one voltage controlling circuit for producing, by detecting a change of the second direct current output voltage, the reset electric current to control the fourth alternating current voltage for negative feed-back; and
wherein the first rectifying circuit is provided with a first switching circuit for producing, by controlling the second alternating current voltage for an ON or an OFF state, synchronizing with a timing of switching in the switching circuit, the first pulsating voltage and wherein the first smoothing circuit is provided with a smoothing capacitor for producing, by smoothing the first pulsating voltage, the first direct current output voltage, so as to supply the first direct current output voltage to a load, a choke coil for storing an electromagnetic energy caused by the first pulsating voltage and a second switching circuit supplying the electromagnetic energy stored in the choke coil to the smoothing capacitor by becoming in an ON state when the first switching circuit is in an OFF state.
In the foregoing, a preferable mode is one wherein the first and second switching circuit are made up of a MOS transistor.
According to a sixth aspect of the present invention, there is provided a multi-outputting switching power supply circuit including:
a direct current power supply section for producing a direct current input voltage;
a switching circuit for producing, by controlling the direct current input voltage for an ON or OFF state based on the input control signal, two or more first alternating current voltages, having a fixed frequency controlled by a control signal and a pulse width corresponding to the control signal;
a plurality of transformers for producing, by transforming the first alternating current voltage, a second alternating current voltage with a fixed voltage value and at least one third alternating current voltage;
a first rectifying circuit for producing, by rectifying the second alternating current voltage, a first pulsating voltage;
a first smoothing circuit for producing, by smoothing the first pulsating voltage, a first direct current output, so as to supply the first direct current output voltage to a load;
a voltage change detecting circuit for producing, by detecting a change of the first direct current output voltage, a detective signal;
a controlling circuit for producing the control signal to control a pulse width of the first alternating current voltage for negative feed-back based on a level of the detective signal;
at least one magnetic amplifier for producing a fourth alternating current voltage with a pulse width corresponding to a reset electric current by controlling the third alternating current voltage for an ON or an OFF state based on the reset electric current;
at least one second rectifying circuit for producing, by rectifying the fourth alternating current voltage, a second pulsating voltage;
at least one smoothing circuit for producing, by rectifying the second pulsating voltage, a second direct current output voltage so as to supply the second direct current output voltage to a load;
at least one voltage controlling circuit for producing, by detecting a change of the second direct current output voltage, the reset electric current to control the second alternating current voltage for negative feed-back; and
wherein the first rectifying circuit includes a switching circuit for producing the first pulsating voltage by controlling the second alternating current voltage for an ON or an OFF state, synchronizing with a timing of switching in the switching circuit.
In the foregoing, a preferable mode is one wherein the switching circuit is made up of a MOS transistor for producing the first pulsating voltage by controlling the second alternating current voltage for an ON or an OFF state, synchronizing with a change of polarity of the second alternating current voltage.
Also, a preferable mode is one wherein the transformer includes an auxiliary winding for producing controlling voltage to control the switching circuit for an ON or an OFF state.
Also, a preferable mode is one wherein the transformer includes an auxiliary winding for producing controlling voltage to control the first and second switching circuit for an ON or an OFF state.
Furthermore, a preferable mode is one wherein the third alternating current voltage has a necessary pulse width to saturate the magnetic amplifier.
With above configurations, because the main-output circuit section is provided with the synchronous rectifying circuit made of the MOS transistor, even if the load becomes light, an abrupt narrowing of time width of an ON state of the MOS transistor does not occur. Therefore, the product of voltage and time (VT) is easily ensured, consequently, direct current output voltage is produced stably. Moreover, because the main-output circuit section does not need a dummy resistor and an electric dummy circuit, an efficiency of a power supply is improved and a number of parts can be decreased. Moreover, because an active clamp circuit is included in the input circuit section so as to obtain a ideal waveform of gate voltage of the MOS transistor, high efficiency is carried out. In addition, because each main-output circuit section and sub-output circuit section is provided with the input circuit section and the transistor, heat can be dispersed, and a multi-outputting power supply circuit can be small and thin. Moreover the number of the sub-output circuit section can be easily increased and decreased on demand.